the screw holding my pillion seat on was a right knut to get out too, an intruder so same design for holding the seat on! I just spentan hour just getting one screw out, little pressure, little tap with a hammer, little squirt of WD40 and repeat..... don't take it to a garage tho, get yourself a tap and die kit from a tool shop and a harder small drill bit, tell the person you buy it off what its for so you can get one that'll drill through a screw! might take a good few hours but it'll save you money and hopefully a get you out of a bollocking from you dad!!!